The sensation of pain is associated with numerous physiological and psychological ailments, and is a universal experience of all complex living organisms. Pain, as the mental manifestation of a neurological response, is an important biological attribute and critical to living and adapting to the environment. Notwithstanding this important role of pain, the alleviation of pain has been a fundamental goal of medicine for as long as the medical profession has existed. Indeed, the ability to control the neurological pathways through which pain is conveyed has made complex procedures far simpler to implement and much less traumatic to the patient.
There is additionally a class of neurological response which is associated with pain that does not correspond to or act as a warning for a particular physical damage or biological dysfunction. In fact, many biologically important transitions are characterized by significant pain, such as the withdrawal period of an addict, during which time the addict's system is depleted of a specific endogenous narcotic. Other mental conditions which are neurological response-dependent conditions include depression, hypertension, causalgia pain, insomnia, and jet lag.
The importance of the ability to control neurological responses and associated perceptions of pain and distress has led to the development of many pain control methodologies. The most common pain control methodologies employ bio-active chemical agents that act to block neurotransmission pathways within the body. These chemicals are designated to operate locally, for spot treatment, or broadly for generalized control or inhibition of the pain response throughout the body. Chemical interference with pain signals has broad based appeal, but in many instances is unacceptable. For example, certain chemicals have toxic side effects or cause allergic reactions in certain patients. For more chronic ailments, such as chronic migraine headache syndrome, continuous absorption of chemical narcotics may reduce the associated pain, but at unacceptably high costs associated with interference with routine activities, addiction, and/or toxicity of the narcotic.
In view of the problems associated with chemical pain control, efforts have focused on treatment approaches which do not involve pharmacological (chemical) interference with neurotransmitters in the body. One such approach involves the use of electrical stimulator devices capable of passing currents across key neurotransmitter junctions in the body, and thus effecting a blockage of neurological pathways which are inducing messages of pain to the brain.
One such electrical stimulator device is the Electreat Transcutaneous Electrical Nerve Stimulator (TENS), manufactured by the Electreat Manufacturing Co., of Minneapolis, Minn. A version of this device was patented in 1919, as U.S. Pat. No. 1,305,725. The Electreat TENS is a therapeutic device which is indicated for the reduction of the symptoms of chronic and acute pain. The device includes a battery power supply, containing two "D" cells connected end-to-end and in series, which delivers 3.0 volts to a coil and interrupter assembly. The interrupter assembly delivers a positive spike waveform which is balanced by a negative long duration low voltage waveform to a transformer, which increases the output voltage level. In the Electreat TENS, the output level may be varied by moving the secondary winding of the transformer in relation to the primary winding of the transformer so as to vary the magnetic coupling between the transformer windings. The output of the Electreat TENS is provided to the tissue of a patient, either directly, using a roller applicator typically associated with the device, or using sponge contact electrodes and cables, which can be connected to the device. It has been found that the electromagnetic structure of the Electreat TENS generates a high voltage spark gap which is a source of a broad range of frequencies, running even into the gigahertz range. The Electreat TENS has been found to be a highly penetrating electrical stimulator for use in relieving acute pain, such as back pain and other post-trauma acute pain episodes of the body. However, the Electreat TENS is a rather large and heavy device, shaped like a long (28 cm) flashlight and weighing over 680 grams.
Another practical implementation of the electrical stimulation approach to pain treatment is disclosed in U.S. Pat. No. 3,902,502, to Liss, et al. The system disclosed in this patent provides a pulsed direct current waveform having a high frequency carrier modulated by a single low frequency modulation. It was discovered that this waveform was particularly successful at controlling symptoms of certain neurological disorders.
U.S. Pat. No. 5,109,847, to Liss, et al., describes an apparatus which generates low current nerve stimulation waveforms to control pain and/or reduce the specific symptoms of certain neurological dysfunctions. This device includes a small DC power source and a means for converting the current output of the power source into a complex waveform as an output across two or more electrodes attached to the patient's body. The complex waveform includes a carrier frequency with at least two low frequency modulations. The carrier frequency ranges between 1 and 100,000 kHz. The first modulation to this carrier has a frequency between 0.01 and 199 kHz. The second modulation to the carrier has a frequency range between 0.1 and 100 kHz. Each modulation to the carrier is pulse trained in the form of a square waveform. This device includes various ancillary systems, such as a low-battery and system-on indicator.